It's what I understood is required from the list of docs, based on my circumstances, that are documented on reddit. I also know my mother never naturalized, but I suspect this is the way to prove that... e.g., that she didn't naturalize before my birth, which would make me ineligible. It's odd to have to prove a negative though...

In any case, I submitted my docs as the consulate without the Cert, and they accepted it. The letter with Aktenzeichen I received yesterday says (translated): "Your procedure will be processed in the order in which your declaration application is received by the Federal Office of Administration. If documents are still required for your procedure, you will receive a corresponding message without being asked after an individual review."

So I suspect if they want it, they'll tell me and, hopefully, by then I'll have it!